The present invention relates to the art of vacuum assemblies of the type in which a vacuum seal must be maintained around the periphery of a shaft which may rotate about and/or move along its longitudinal axis.
In one assembly the shaft is hollow and the vacuum is drawn through the shaft. Such rotating vacuum shaft assemblies are used in many applications, glass shaping being a typical application. Typically, glass is shaped by the application of heat as it rotates on a suitable machine, such as a lathe. The glass is located around a mandrel which is turned on the lathe. As heat is applied to the glass, it becomes pliable. To form the glass into the shape of the mandrel it is advantageous to reduce the pressure within the volume of the glass so that the pressure difference across the glass causes the glass to conform in shape to the mandrel. Thus, some type of rotating vacuum shaft assembly is needed; typically the assembly is mounted on the lathe tail stock so that the vacuum is transmitted to the mandrel via a rotating shaft. A vacuum pump is connected to the assembly so that the vacuum is drawn through the end of the shaft mounted on the assembly.
Such assemblies are not, per se, novel. One known assembly uses an O-ring seal with vacuum grease, the O-ring seal being located on either side of the pumping orifice. This seal requires some pressure to be exerted on the shaft thereby making the shaft not as free turning as is desirable in some applications. Also, this seal has been found to not create an adequately high vacuum for some requirements especially in glass shaping.
Another known assembly uses a neoprene seal which is mounted on the rotating shaft via metal washers affixed on either side of the seal and to the shaft itself. The seal has a curved outer member which contacts the internal wall of the housing. This type of assembly has been found not to be adequately free turning and capable of high vacuums.